Transcript Strong Lensing Studies at Fermilab

Strong Lensing Studies at
Fermilab
Elizabeth Buckley-Geer for the
Experimental Astrophysics Group
Fermilab Center for Particle Astrophysics
April 2007
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Collaborators
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Fermilab: H. Lin, D. Kubik, H.T. Diehl, S. Allam, D. Tucker, E.
Buckley-Geer, J. Kubo, J. Annis, J. Frieman, D. Finley, J.
Estrada, D. McGinnis, V. Scarpine, … Fermilab Cosmology
Analysis Group
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D. Schneider, M. Oguri, A. Shapley, A. Baker, D. Lutz, J.A.
Smith, J. Brinchmann, M. Strauss, M.-S. Shin, C. Kochanek,
C. Tremonti, …
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Outline
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SDSS Arc Search
Follow-up Observations
Sample Properties
Lens Modeling for LRG-4-606
A lens from the BCS data
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SDSS Arc Search
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The candidates come from two different samples.
► Potential red galaxy lenses from SDSS DR5 (8000 deg2)
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221,000 luminous red galaxies (LRGs)
29,000 brightest cluster galaxies (BCGs) from maxBCG cluster sample (J. Annis)
SDSS DR5 CAS database query (D. Kubik)
– Blue galaxies (g-r and r-i color cuts)
– < 10” from LRG or BCG
– 57,000 systems returned with n=1 or more blue objects
– Rank systems by number of blue objects n
Visual inspections
– Inspect all systems (1081) with n ≥ 3 blue objects
– 4 separate inspectors looked at SDSS CAS gri color jpeg images
– Follow up 14 candidate systems flagged by 2 or more inspectors
– Plus 1 more (“clone”) from single-inspector eye scan of n=2 LRG list
► Interacting-merging galaxy sample (S.Allam)
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Start with 15,000 isolated galaxies and 38,000 isolated galaxy pairs from SDSS DR5
Exclude spiral galaxies to avoid false detections of lenses
Apply additional selection cuts.
Yields 17500 objects which after visual examination reduces to 3000 objects.
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Follow-up Observations
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The search identified N candidate systems
Follow-up observing program (Fermilab group) on Apache
Point Observatory (APO) 3.5m telescope
► Arcs are bright (r ~ 20-22) and high SB (r ~ 23-24 mag/arcsec2)
► SPIcam gri imaging (15 min exposures per filter) for deeper images
(SDSS discovery images are only 54 seconds on a 2.5m telescope)
► DIS spectroscopy (45 min exposures) of brighter targets for source and
lens redshifts
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We curently have 9 spectroscopically confirmed lensing
systems.
► 6 with z ≥ 2
► 3 have z ~1.0
► Lenses typically have z ~ 0.4
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We also have HST and Spitzer data for one system
(lrg_2_2811)
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9 Spectroscopically Confirmed
Lensing Systems
April 2007
lrg-3-817
zl = 0.35
zs = 2.26
SSA_1113
zl = 0.35
zs = 0.77
lrg-3-227
zl = 0.45
zs = 0.98
lrg-2-2811
zl = 0.42
zs = 2.0
“The Clone”
lrg-4-581
zl = 0.43
zs = 0.97
“Cosmic
Snowman”
lrg-3-757
zl = 0.44
zs = 2.38
“Cosmic
Horseshoe”
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lrg-4-606
zl=0.49
zs = 2.03
8 o’clock arc
zl = 0.38
zs = 2.73
SSA_1343
zl = 0.34
zs = 2.1
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Example Spectra
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Comparison of SDSS, Subaru
and HST Data for lrg-2-2811
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Spitzer Data for lrg-2-2811
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Lens Modeling Results for
lrg-2-2811- ‘The Clone’
•Using LENSVIEW (R. Wayth & R.L. Webster, MNRAS 372
(2006) 1187-1207).
•Assume a SIE mass profile
•Flat cosmology, Wm=0.3, WL=0.7, H0=100 h km s-1 Mpc-1
•Fit for the Einstein radius θEIN
Model Image
Source
Residuals
Tangential caustic
Tangential
Critical curve
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Modeling for lrg-4-606
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Use GALFIT to model the light profiles of the galaxies and
the arcs
Input
Residuals
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Model
i band
Combination of Sersic profiles for the
galaxies and exponential disks for the arcs
18 objects + sky
χ2/dof = 1.4
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GALFIT r-band
Residuals
Model
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Input
Use i-band parameters for galaxies
and allow magnitude and position to
vary. Allow all arc parameters to
vary.
Add small red galaxy that is visible
at the top left of the arc (it shows up
most clearly in r).
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GALFIT g-band
Residuals
Model
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Input
Use i-band parameters for galaxies
and allow magnitude and position to
vary. Allow all arc parameters to
vary.
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Color-magnitude plot
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LENSVIEW Input
Use g-band image
Add small red galaxy at correct location
using g-band magnitude estimated from
color-magnitude plot
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First try using Lensview
Input
Model
SIE
θEIN = 7.4”
Axis ratio = 0.77
PA = 44.7°
Source
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BCS data – Elliot Arc
Parameters (using
Lensmodel)
θEIN = 7.5"
Ellipticity = 0.269
PA = -32.8 deg
χ2/dof = 1.03
σ = 826 km s-1
REIN = 28.2 h-1 kpc
MEIN = 1.4x1013 h-1 M
A4
A1
A2
A3
The galaxy cluster surrounding the arc has
an Ngals ≥ 71 and a mass of M200 ~ 4x1014 h-1
M which makes it a very rich cluster. GMOS
spectra taken with Gemini South in August
2007 give zl = 0.38 and zs = 0.9
April 2007
This system is included in a
recent proposal that we submitted
to get HST imaging data.
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